Alternate fuels have been developed to mitigate the rising prices of conventional fuels and for reducing exhaust emissions. For example, natural gas has been recognized as an attractive alternative fuel. For automotive applications, natural gas may be compressed and stored as a gas in cylinders at high pressure. A pressure regulating valve may then be used to supply the compressed natural gas (CNG) at lower pressures to an engine combustion chamber. Various engine systems may be used with CNG fuels, utilizing various engine technologies and injection technologies that are adapted to the specific physical and chemical properties of CNG fuels. For example, mono-fuel engine systems may be configured to operate only with CNG while multi-fuel systems may be configured to operate with CNG and one or more alternate fuels, such as gasoline or gasoline blend liquid fuels.
However, the inventors herein have recognized a potential issue with such systems. There may be conditions when a fuel rail pressure of the CNG fuel line is too high, for example, due to degradation of a fuel line pressure regulator, an internal leak in a regulator valve, a breach in a regulator diaphragm, a regulator valve being stuck open, a tank valve stuck open, etc. Prolonged exposure to high fuel rail pressures can damage the fuel injectors and lead to reduced injector flow. While some pressure regulators may include a venting valve to enable pressure relief, such venting can create a stream of venting fuel on the vehicle. In all such cases, fuel economy and vehicle performance is degraded.
The inventors herein have recognized that various different conditions may lead to elevated fuel line pressures and without knowing the cause of the elevated fuel rail pressure, appropriate mitigating steps may not be taken. Additionally, since bi-fuel systems can be operated in various different operating modes, routines diagnosing elevated CNG fuel rail pressures may need to factor in whether the CNG fuel is in use or not in use.
In one example, some of the above issues may be at least partly addressed by a method of operating a fuel system configured to deliver a gaseous fuel to an engine. In one embodiment, the method comprises, during selected conditions, sequentially opening a tank valve and a fuel rail valve of the fuel system, and indicating degradation of a pressure regulator of the fuel system based on a change in fuel rail pressure during the sequential opening. In this way, a rise in fuel rail pressure may be better diagnosed and accordingly addressed.
For example, a fuel system coupled to a vehicle engine may be configured to deliver a gaseous fuel, such as CNG, from a fuel tank to the engine via a fuel rail. As such, the gaseous fuel may be stored in the fuel tank at high pressure and delivered though a solenoid fuel tank valve to a fuel line, wherefrom the fuel is delivered to the fuel rail at a controlled pressure upon passage through a pressure regulator. The pressure regulator may include various components including at least a mechanical pressure regulator component and a duty-controlled solenoid fuel rail valve.
During conditions when the gaseous fuel is not in use, such as when a second fuel (e.g., gasoline fuel) is available and in use, or when the engine is not running, diagnostic routines may be performed to verify that the various components involved in regulating the pressure of the gaseous fuel are functional. The diagnostic routines may involve sequentially opening the fuel tank valve and the fuel rail valve and observing changes in a fuel rail pressure during the course of the sequential opening. For example, the tank valve may be opened and a change in fuel rail pressure may be observed before the fuel rail valve is opened. As another example, the tank valve may be opened while an opening of the fuel rail valve may be regulated to a target (higher) pressure, and a change in fuel rail pressure may be observed before the fuel rail valve is fully opened. Based on the observed changes in fuel rail pressure, degradation of the mechanical regulator, fuel rail valve, or tank valve may be determined. Accordingly appropriate mitigating actions may be taken. For example, if the mechanical regulator is degraded, gaseous fuel rail pressure may be controlled using the fuel rail valve, or vice versa. As another example, if both the mechanical regulator and the fuel rail valve are degraded, gaseous fuel rail pressure may be controlled using the tank valve. As such, if a gaseous fuel rail over-pressure condition persists when the gaseous fuel is in use, the tank valve may be closed and optionally, engine operation may be temporarily switched to the alternate available fuel, to reduce over-pressure induced degradation of fuel system components.
By better identifying pressure regulator component degradation and performing mitigating actions accordingly, fuel rail pressure of a gaseous fuel may be better controlled even if some components involved in pressure regulation are degraded. In particular, fuel rail over-pressure conditions may be reduced. By shutting off a tank valve in response to over-pressure of a fuel rail delivering the gaseous fuel to an engine, fuel wastage due to fuel venting may be reduced, while also reducing component damage from prolonged exposure to elevated fuel rail pressures. Overall, usage of the gaseous fuel and vehicle fuel economy may be improved.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.